I. Field
The following description relates generally to communication systems and more particularly to a low receiver complexity approach for reliable packet decoding when Hybrid ARQ (H-ARQ) protocol is employed with persistent assignment and an optional erasure sequence transmission.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long-Term Evolution (LTE) systems, orthogonal frequency division multiple access (OFDMA) systems, as well as others.
Typically, most communication systems ensure reliable exchange of data by employing an error control method such as a Hybrid ARQ (H-ARQ) protocol. H-ARQ protocols are commonly employed along with persistent assignment and optional erasure sequence transmission over small bandwidth channels with low throughput traffic such as VOIP (Voice over Internet Protocol) networks. H-ARQ techniques increase complexity of the system but can provide significant improvement in capacity. With Hybrid ARQ, a packet is sent using multiple transmissions. The packet transmission could be terminated early if the receiver can decode the packet prior to receiving the entire transmission. However, in order for early termination, the receiver (or recipient) must provide some acknowledgement that the data was received.
In order to make the communication between systems more efficient, a concept of persistent assignments is used. Persistent assignments are useful in a scheduled data transmission system in cases where many users are competing for limited assignment message resources. A persistent assignment occurs when a resource (e.g., a channel) that is assigned to a particular user (e.g., user device) continues to be available to that user after transmission of a data packet is completed. Thus, a new assignment message is not necessary to enable a user to continue transmission between the two systems.
The above can be achieved by optionally transmitting a low power sequence, such as an erasure sequence, when data is not being transmitted over the channel. The erasure sequence aids in notifying a receiver that a transmitter is likely to transmit another data packet over the channel. In this manner, the receiver does not end the communication process or assume that a link has failed. Thus, the transmitter can continue to communicate with the receiver and transmit the next data packet after the erasure sequence.
Typically, in advanced high-speed data communication systems employing H-ARQ protocol with persistent assignment, the optional erasure sequence is sent as a keep-alive indication when there is temporarily no data to transmit. The erasure sequence, however, is sent at a small fraction of the normal transmit power level since the erasure sequence only contains a single information bit, and as a result may suffer unreliable detection at the receiver, especially if the assignment has small bandwidth. This can cause problems at the receiver because failure to recognize the start of packet (SOP) prevents the packet from being correctly decoded, implying reduced throughput and increased latency jitter or data loss depending on whether the application enables upper layer re-transmission.
Conventional systems employ various methods in an attempt to solve the above mentioned problem. One attempted solution is to directly improve erasure detection reliability by increasing transmission power. However, increased transmission power can lead to an increased level of interference. Another attempted solution is to improve SOP determination reliability, despite unreliable erasure detection, by attempting multiple SOP hypotheses at the cost of receiver complexity. Another attempted solution method includes avoiding erasure detection altogether by sending filler data from upper layer at the cost of transmitter complexity for cross-layer coordination, increased level of interference, and can shorten battery life. The approaches presented by conventional systems in an attempt to solve the reliability issue of packet decoding increase resource consumption and overall complexity of the system.